A power module 70 used in an inverter for a vehicle is conventionally composed of electronic components shown in FIG. 7. Specifically, the power module 70 includes at least a power element 71 composed of a silicon element, an insulating member 73 composed of aluminum nitride and to which the power element 71 is fixed via a solder layer 72, and a heat sink member 74 composed of aluminum. Moreover, a cushion member 75 composed of copper-molybdenum (Cu—Mo) or aluminum-silicon carbide (Al—SiC) is disposed between the insulating member 73 and the heat sink member 74. The cushion member 75 is provided in order both to transfer and radiate heat generated by the power element 71 to the heat sink member 74 for radiation and to reduce the difference in thermal expansion between the insulating member 73 and the heat sink member 74. The cushion member 75 is fixed to the insulating member 73 by a solder layer 76 and to the heat sink member 74 by silicon grease 77. Thus, the cushion member 75 and the heat sink member 74 are configured as a heat transfer member for radiating heat from the power element 71.
However, in the power module 70, the silicon grease 77, fixing the cushion member 75, has a lower heat conductivity than the other members and thus disturbs the transfer of heat from the power element 71 to the heat sink member 74. To avoid this, for example, it is expected to be desirable to thermally spray copper-molybdenum (Cu—Mo) directly onto the surface of the heat sink member 74 without using the silicon grease 77, thus forming the cushion member 75 as a coating film.
On the other hand, in recent years, a coating film formation method called a cold spray method has been proposed. The cold spray method uses a convergent and divergent (Laval) nozzle to increase the flow velocity of gas heated to a temperature lower than the melting point or softening temperature of a material for a coating film. The method then introduces metal powder, a material for the coating film, into the gas flow to accelerate the flow. Thus, the metal powder collides against a base material at a high speed while remaining in the solid state, to form a coating film. As an example of the cold spray method, a method has been proposed which compresses very expansive helium gas or nitrogen gas and sprays the metal powder onto the surface of the base material together with the compressed gas, with the metal powder remaining in the solid state, thus forming a coating film with the composition of the powder (see, for example, Patent Document 1).
Patent Document 1; JP Patent Publication (Kokai) No. 2004-76157